Bentonite mainly comprising a mineral clay montmorillonite is typical of smectite clays. It has outstanding swelling power or dispersibility in water, increasing in volume several times as much as its own volume on being swollen with water, to form a semi-solid gel or a highly viscous colloidal dispersion. However, the medium in which bentonite exhibits such high swelling power or dispersibility is confined to a fresh water system containing no or little electrolyte, and there has been no technique for swelling smectite clays such as bentonite with an aqueous electrolyte solution containing an inorganic electrolyte in a high concentration, such as a brine (e.g., seawater), a mortar/water system or a concrete/water system. A conventional method for dispersing smectite clays, e.g., bentonite in such an aqueous electrolyte solution comprises swelling a smectite clay with fresh water, followed by dispersing, and adding to the dispersion an anionic surface active agent, such as a sodium alkylsulfate, a sodium alkanesulfonate or sodium humate; a condensed phosphate, such as tetrasodium pyrophosphate or sodium hexametaphosphate; or a polyelectrolyte, such as sodium polyacrylate or a partial hydrolysis product of polyacrylamide, to increase the electrostatic repulsive force among the clay particles thereby dispersing the particles to colloidal particles. Since the dispersion obtained in this manner has insufficient viscosity, it has been a practice followed when a high viscosity is required as is usual to increase the viscosity to a desired level by addition of a large quantity of an expensive substance, such as xanthan gum. For the time being, there is no means available for letting a smectite clay fully exhibit its characteristic swelling power in an aqueous electrolyte solution. For example, Nature, Vol. 173, No. 4397, pp. 255-256 (1954) contains an article entitled "Crystalline Swelling of Montmorillonite--Use of Electrolyte for Swell Control", which elucidates that the swelling of sodium montmorillonite in an aqueous sodium chloride solution having a concentration of not less than 0.3N (about 1.8% on a mass basis) is limited crystalline swelling.
While the characteristic of smectite clays which is advantageously used in industry is the so-called osmotic swelling attended by remarkable volume expansion far beyond crystalline swelling, smectite clays cannot exhibit the osmotic swelling in an aqueous electrolyte solution due to the dehydrating effect and charge neutralizing effect of an electrolyte on colloidal particles.
S. Olejnik, A. M. Posner and J. P. Quirk, Clays and Clay Minerals, Vol. 22, pp. 361-365 (1974) examined swelling of montmorillonite in a polar organic liquid whose dipole moment is approximate to that of water and whose relative permittivity is higher than that of water and reported that montmorillonite shows the osmotic swelling only in formamide HCO-NH.sub.2 and N-methylformamide HCO-NH(CH.sub.3). However, the present inventors have confirmed that these liquids have no effect to activate smectite clays so as to exhibit the osmotic swelling in an aqueous electrolyte solution. These organic solvents, while having a high relative permittivity, are protonic solvents as is apparent from their molecular formulae and are therefore assumed to behave like water to an electrolyte.
Organic ammonium bentonite obtained by cation exchange treatment of bentonite with a long chain fatty ammonium ion, e.g., an octadecylammonium ion can be activated by addition of a low-molecular weight highly polar substance, such as methanol or ethanol, and is thereby made substantially swellable with an organic liquid, as reported in R. E. Grim, Clay Mineralogy, p. 266, McGraw-Hill Book Co., Inc., (1953). Nowadays organic ammonium bentonite, called organophilic bentonite, is commercially supplied as a thickener for organic solvent type paints or printing inks or a gelatinizer for lubricating grease under the trade name of "Organite" (manufactured by Nihon Yuki Nendo K.K.), "S-Ben" (manufactured by Nihon Yuki Nendo K.K.), "Orben" (manufactured by Shiraishi Kogyo K.K.), "Bentone" (manufactured by Rheox Inc., U.S.A.) or "Claytone" (manufactured by Southern Clay Products, Inc.). In using such organophilic bentonite, a combined use with a highly polar additive, such as methanol, ethanol, acetone or propylene carbonate, has been widespread. However, being utterly water-repellent, the organophilic bentonite is applicable only to middle to low polar organic liquids, such as mineral spirit, toluene, xylene, dioctyl phthalate, and petroleum lubricating oils, and is essentially non-wettable, non-swellable and non-dispersible with an aqueous electrolyte solution such as a brine or a cement slurry.
Swelling power and colloidal dispersibility of bentonite in a fresh water system has been utilized as a soil-drilling stabilizing fluid in civil engineering work or as a drilling fluid in drilling of an oil well, a geothermal well, a well, etc. However, the bentonite soil-drilling stabilizing fluid or drilling fluid undergoes serious deterioration when in contact with a salty underground water (i.e., a brine) in offshore-drilling on a continental shelf or a coastal area.
Bentonite has been used in a cement grout for preventing sedimentation of cement, but bentonite particles undergo flocculation due to an alkali eluted from cement, making it difficult to control the fluidity of the grout. Further, it has been impossible to incorporate bentonite into a cement grout in a high concentration for improving sealing properties.
Swellable clays such as bentonite are of extreme importance as a component for making ground impervious to water, and are utilized as a sealant for prevention of water leakage from the side walls or bottoms of paddies, reservoirs, and ponds. They also have found their use as an impervious layer-forming soil conditioner for prevention of pollution with water from landfills of industrial wastes. In every application, they are effective only on fresh water, and their water impermeability is not sufficient against attack of a brine, such as seawater.
A technique of laying geosynthetic clay liners is used for protection of underground structures from penetration of underground water, the geosynthetic clay liners being a laminated material composed of a geomembrane made of a durable synthetic resin and a layer of fine bentonite particles. When used in sites subject to the attack of a brine such as seawater, the geosynthetic clay liners must be swollen with fresh water beforehand, making it difficult to carry out the technique.
The aforesaid practical disadvantages of smectite clays are attributed to the fact that a clay mineral smectite, the main component of smectite clays, belongs to hydrophobic colloid and, in nature, is flocculated by the action of an electrolyte and does not become colloid.